1. Field of the Invention
The present invention relates to a UV absorbing material with the property of a radical reacted crosslinking agent and the use of such a compound to manufacture UV absorbing soft contact lenses. More particularly, the invention relates to a material having UV absorbing moiety and multiple reactive vinyl groups that can be used to replace conventional crosslinking agents and UV absorbing agents incorporated in the hydrophilic soft contact lenses.
2. The Prior Arts
The UV part of the sunlight that reaches the earth surface consists mostly the radiations with wavelength between about 290 and 400 nm. The UV having short wavelengths below 175 nm is absorbed by oxygen at latitude of about 100 km whereas the radiations between 175 and 290 nm are mostly absorbed by the ozone layers about 15 km above the sea level. However, some UV radiations below 290 nm may still reach the earth surface because of the ozone depletion caused by the environmental pollution. It is well recognized that exposure to ultraviolet radiation is damaging to the cornea and is resulting in ocular pathology. As a result, a great concern is focused on providing adequate ocular protection against UV radiation and protecting people who are liable to UV exposure, for example, patients who have cataract surgery or take photosensitizing drugs.
The addition of UV absorbing compounds in the contact lenses or intraocular lenses to minimize detrimental effect of UV radiation by absorbing UV light in the region of 290 to 400 nm is well known. Many different processes have been disclosed to produce UV absorbing contact lenses or spectacles. For example, the UV absorbing property can be obtained by adding high molecular weight or water insoluable UV absorbing chemicals in lens formulation. However, to prevent leaching of the UV absorber from the lenses during various service environments, the reactive UV absorber that can be copolymerized with the lens material is usually preferred.
In general, lenses are prepared by the free radical polymerization of the lens forming monomers. The constituents in the formulation can be modified to produce lenses with required water content and other physical properties. Copolymerizable UV absorbers are usually directly incorporated in the lens formulation. Methods based on the above process for preparing reactive monomeric UV absorbing compounds can be found in U.S. Pat. Nos. 3,162,676, 3,213,058, 4,304,895, 4,310,650, and 4,528,311. For example, in U.S. Pat. Nos. 4,304,895 and 4,528,311, UV absorbers are functionalized with both UV absorbing moiety and reactive vinyl group that can copolymerize with different acrylic monomers to form contact lenses. Usually, lenses are polymerized in these processes by thermal initiated free radical reaction rather than UV-photo initiated reaction because of the interference of the initiation step by the presence of UV absorbers. Although photo polymerization is also employed in formulations using some of these UV absorbers, a low degree of conversion is usually obtained and the unreacted residual UV absorbing agent in the cured lens must be removed by a subsequent cleaning procedure.
With regard to the thermal initiated process in forming contact lenses, the as-known shortage arises from its relatively long processing cycle that is needed to obtain a lens with a good quality. Consequently, the other alternative-photo polymerization has been proposed to manufacture UV absorbing contact lenses. For example, U.S. Pat. No. 5,098,445 discloses a contact lens with UV absorbing agent covalently bonded after the lens is photo polymerized. The UV absorber is reacted with the hydroxyl group in the formed lens by dipping the lens in an aqueous solution having dissolved halotriazine compound with UV absorbing moiety under alkaline condition. A similar process is also disclosed in U.S. Pat. No. 5,399,692. Yet, it is argued that the triazinyl molecule is detrimental to the physical and optical properties of the lens. Uncertainty in the degree of reaction during the bonding step of halotriazine with the lens materials also arises, which limits the application of the technique.
U.S. Pat. No. 5,914,355 discloses a process to prepare an UV absorbing contact lens after the lens is photo cured. In the process, a derivative of the UV absorbing benzotriazole compound is transformed into a non-UV absorbing material by replacing the hydroxyl group of the phenol moiety with a convertible protective group. This essentially non-UV absorbing agent with reactive vinyl group is added in the lens-forming monomer mixture and photo cured. The formed lens is then changed to be UV absorbing by converting the protective group beck to a hydroxyl moiety in an alkaline environment. This conversion process requires a series of tedious reaction processes. To overcame this shortage, U.S. Pat. No. 5,945,465 discloses a similar process but using the photo-Fries rearrangement to deactivate the protective group during UV exposure. Yet, there are still uncertainties in the degree of conversion in the deactivating step.
U.S. Pat. Nos. 5,681,871 discloses a benzophenone UV absorber with modified reactive anhydride group that can be covalently bonded with the hydroxyl group in the as-formed lens under basic condition. The UV absorbing agent can be applied before or after the lens is photo cured. However, the hydration procedure used to bond anhydride with hydroxyl groups is also relatively time-consuming.
A photo cured UV absorbing agent that required no additional bonding step is disclosed in U.S. Pat. No. 4,719,248. The benzotriazole type UV absorber is modified to have a reactive vinyl group and is claimed to be covalently bonded with the lens-forming monomers by photo polymerization without noticeable yellowness and interference of the curing reaction. Yet a low yield is obtained during the synthesis of the modified UV absorber. In addition, a relatively long photo curing time is required due to the use of photo initiator with active wavelength in the region of visible light.
To obtain a high UV absorption ability, the use of the dual UV absorption compounds that absorb UV in different wavelengths was proposed. In U.S. Pat. No. 4,963,160, a method of bonding two UV compounds with different UV absorbing spectra onto a triazine derivative was proposed. The proposed UV absorption compound requires multiple synthesis procedures to accomplish and needs an additional bonding step to react with the as-formed lens. A similar invention is disclosed in U.S. Pat. No. 6,244,707 in which both benzophenone and benzotriazole derivatives with different UV absorbing power but all containing the mono vinyl group are copolymerized with the lens forming materials to have a strong UV blocking property.
In summary, these UV absorbers usually suffer one or some of the undesired nature such as long reacting time, low conversion, uncertainty in the degree of reaction, leach of unreacted UV absorber, yellowness, inconsistent integrity of the formed lens, expensive reactant used, and tedious reacting process. Henceforth, there exists a need for preparing an improved UV absorbing compound without the aforementioned shortages.